Complex Aquifer System Research Articles

Investigations of natural attenuation in groundwater near a landfill and implications for landfill post-closure

The controlled landfill technology is now adopting passive attenuation techniques as an increasing number of landfill sites reach the post-closure phase. During the post-closure phase, landfill operators need to convince environmental authorities that landfills no longer pose a threat to health or the environment. The demonstration of acceptable risk should rely in particular on data collected during environmental monitoring in addition to modelling of possible future evolutions of environmental concentrations. One difficulty that is typically encountered in France is related to the fact that groundwater monitoring systems around landfills are often insufficiently detailed to provide conclusive evidence of natural attenuation mechanisms. This paper presents data on groundwater quality in the vicinity of an old landfill located in a complex aquifer system. While isotopic data show a signature of the landfill leachate in the groundwater in the vicinity of the landfill, chemical analyses do not suggest a strong influence, which could be indicative of natural attenuation mechanisms in the groundwater. However, the complexity of the groundwater system in this area is such that it cannot be excluded that a pollutant flux is being overlooked. Implications of demonstrating natural attenuation during the landfill post-closure phase, with respect to groundwater monitoring, are discussed.

Multi-tracer tests to evaluate the hydraulic setting of a complex aquifer system (Brévilles spring catchment, France)

For good management of groundwater resources, and to comply with European and national regulations, a detailed understanding of an aquifer’s hydraulic setting is required. In order to better characterize a sandy aquifer that is affected by diffuse pollution (Brevilles spring catchment, Val d’Oise, France), and to quantify the transfer time in the saturated zone, a multi-tracer test involving a new technique, the ‘finite volume point dilution method’, has been performed in natural flow conditions. In November 2005, injections of four different tracers took place in four piezometers involving different locations and depths in the aquifer. Recovery of the tracers was observed at two different places near the aquifer outlet. A particularly long and unusual monitoring exercise (27 months) demonstrated the existence of several different velocities within the sandy layer, which seems to be linked to the decrease of hydraulic conductivity with depth. The new insight and parameter quantification brought by interpretation of these tests contribute to a better characterization of the saturated zone. The particularly long-term monitoring exercise also gives new information to understand and forecast the trend and persistence of groundwater contamination by pesticides in the catchment.

Determining The Salt Store and Mobility in the Regolith, Bland Sub-Catchment, Central Nsw

To manage salinity risk for a sub-catchment or a region, quantifying the salt store and degree of salt mobility are two fundamental issues to address. In a thick (e.g. 70 m) and complex aquifer system, where sand bodies are semi-confined to confined within spatially dominating mud and clay, quantifying the salt store and mobility based on information collected from sparsely and unevenly distributed water bores and exploration drill holes is a significant challenge. Airborne electromagnetic (AEM) data, using Fugro?s time-domain TEMPEST fixed wing system, were collected over ~ 1,500 km2 of the Bland sub-catchment in central NSW (Lawrie et. al., 2002). Conductivity responses depict the electrolyte concentrations (mainly sodium chloride) and water content of the regolith and basement rock (Lawrie et al., 2002). Statistical analyses of water content, salinity and electrical conductivity logs show that conductivity is a measure of salt load. Non-porous bedrock is resistive whereas porous and moist sediments with saline pore fluids are conductive. Amongst the sediments, less porous coarse textured palaeo-valley basal gravely sand is less conductive than highly porous clay-rich colluvium and lacustrine mud. Using conductive depth slices (CDI), the spatial salt load distribution was mapped and quantified using ArcGIS (Tan et al., 2005a).

Identification of groundwater flow paths in complex aquifer systems

AbstractA methodology was developed and applied to the Tindouf (southwestern Algeria) and the Annaba–Bouteldja aquifers (northeastern Algeria) in order to understand better the hydrogeology of the complex aquifers despite the scarcity of the available data. Graphical representation of deuterium versus oxygen‐18 and principal components analysis (PCA) are statistical techniques used to combine various disciplinary data in order to identify chemical and isotopic groups, which are in turn used to define groundwater flow paths. The results of this study agree with the generally accepted hydrogeological conceptual model of the aquifers. In addition, we obtained new results using the PCA method: (1) a description of the complex flow system by grouping various qualitative and quantitative parameters; (2) the definition and characterization of the main groundwater flow paths from their sources to the discharge zones. These flow paths are defined by their water categories, which are represented by salinity and origin of groundwater. This approach is useful for analysing aquifers despite the lack of important database and may also be helpful for studying other complex groundwater basins. Copyright © 2006 John Wiley & Sons, Ltd.

Groundwater nitrate pollution in the Essaouira Basin (Morocco)

The Essaouira Basin (Morocco) contains a multi-layered aquifer situated in fractured and karstic materials from the Middle and Upper Cretaceous (the Cenomanian, Turonian and Senonian). Water percolates through the limestone and dolomite formations of the Turonian stage either through the marls and calcareous marls of the Cenomanian or through the calcareous marly materials of the Senonian. The aquifer system may be interconnected since the marl layer separating the Turonian, Cenomanian and Senonian aquifers is thin or intensively fractured. In that case, the water is transported through a network of fractures and stratification joints. This paper describes the extent of the nitrate pollution in the area and its origin. Most of the wells and drillholes located in the Kourimat perimeter are contaminated by nitrates with some concentrations over 400 mg 1(-1). Nitrate contamination is also observed in the surface water of the Qsob River, which constitutes the natural outlet of the multi-layered complex aquifer system. In this area, agriculture is more developed than in the rest of the Essaouira Basin. Diffuse pollution of the karstic groundwater body by agricultural fertiliser residues may therefore partially explain the observed nitrate pollution. However, point pollution around the wells, springs and drillholes from human wastewater, livestock faeces and the mineralisation of organic debris close to the Muslim cemeteries cannot be excluded. (C) 2003 Academie des sciences. Published by Editions scientifiques et medicales Elsevier SAS. All rights reserved.

Hydrostratigraphic modeling of a complex, glacial-drift aquifer system for importation into MODFLOW.

Deposition from at least three episodes of glaciation left a complex glacial-drift aquifer system in central Illinois. The deepest and largest of these aquifers, the Sankoty-Mahomet Aquifer, occupies the lower part of a buried bedrock valley and supplies water to communities throughout central Illinois. Thin, discontinuous aquifers are present within glacial drift overlying the Sankoty-Mahomet Aquifer. This study was commissioned by local governments to identify possible areas where a regional water supply could be obtained from the aquifer with minimal adverse impacts on existing users. Geologic information from more than 2,200 existing water well logs was supplemented with new data from 28 test borings, water level measurements in 430 wells, and 35 km of surface geophysical profiles. A three-dimensional (3-D) hydrostratigraphic model was developed using a contouring software package, a geographic information system (GIS), and the 3-D geologic modeling package, EarthVision. The hydrostratigraphy of the glacial-drift sequence was depicted as seven uneven and discontinuous layers, which could be viewed from an infinite number of horizontal and vertical slices and as solid models of any layer. Several iterations were required before the 3-D model presented a reasonable depiction of the aquifer system. Layers from the resultant hydrostratigraphic model were imported into MODFLOW, where they were modified into continuous layers. This approach of developing a 3-D hydrostratigraphic model can be applied to other areas where complex aquifer systems are to be modeled and is also useful in helping lay audiences visualize aquifer systems.

Brittle structures and their role in controlling porosity and permeability in a complex Precambrian crystalline-rock aquifer system in the Colorado Rocky Mountain Front Range

Research Article| November 01, 2003 Brittle structures and their role in controlling porosity and permeability in a complex Precambrian crystalline-rock aquifer system in the Colorado Rocky Mountain Front Range Jonathan Saul Caine; Jonathan Saul Caine 1U.S. Geological Survey, P.O. Box 25046, MS 973, Denver, Colorado 80225, USA Search for other works by this author on: GSW Google Scholar Stephanie R.A. Tomusiak Stephanie R.A. Tomusiak 2Department of Geological Sciences, Campus Box 250, University of Colorado, Boulder, Colorado 80309, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2003) 115 (11): 1410–1424. https://doi.org/10.1130/B25088.1 Article history received: 14 Dec 2001 rev-recd: 08 Nov 2002 accepted: 08 May 2003 first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jonathan Saul Caine, Stephanie R.A. Tomusiak; Brittle structures and their role in controlling porosity and permeability in a complex Precambrian crystalline-rock aquifer system in the Colorado Rocky Mountain Front Range. GSA Bulletin 2003;; 115 (11): 1410–1424. doi: https://doi.org/10.1130/B25088.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Expansion of the Denver metropolitan area has resulted in substantial residential development in the foothills of the Rocky Mountain Front Range. This type of suburban growth, characteristic of much of the semiarid intermountain west, often relies on groundwater from individual domestic wells and is exemplified in the Turkey Creek watershed. The watershed is underlain by complexly deformed and fractured crystalline bedrock in which groundwater resources are poorly understood, and concerns regarding groundwater mining and degradation have arisen. As part of a pilot project to establish quantitative bounds on the groundwater resource, an outcrop-based geologic characterization and numerical modeling study of the brittle structures and their controls on the flow system was initiated. Existing data suggest that groundwater storage, flow, and contaminant transport are primarily controlled by a heterogeneous array of fracture networks. Inspections of well-permit data and field observations led to a conceptual model in which three dominant lithologic groups underlying sparse surface deposits form the aquifer system—metamorphic rocks, a complex array of granitic intrusive rocks, and major brittle fault zones. Pervasive but variable jointing of each lithologic group forms the “background” permeability structure and is an important component of the bulk storage capacity. This “background” is cut by brittle fault zones of varying structural styles and by pegmatite dikes, both with much higher fracture intensities relative to “background” that likely make them spatially complex conduits. Probabilistic, discrete-fracture-network and finite-element modeling was used to estimate porosity and permeability at the outcrop scale using fracture network data collected in the field. The models were conditioned to limited aquifer test and borehole geophysical data and give insight into the relative hydraulic properties between locations and geologic controls on storage and flow. Results from this study reveal a complex aquifer system in which the upper limits on estimated hydraulic properties suggest limited storage capacity and permeability as compared with many sedimentary-rock and surficial-deposit aquifers. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Water temperature and conductivity variability as indicators of groundwater behaviour in complex aquifer systems in the south‐east of Spain

AbstractGroundwater temperature and electrical conductivity logs were applied in this study to gain an understanding of the hydrogeological behaviour of a complex system. This system, compartmentalized by a large number of fractures, which may even cause geothermal anomalies, is that of the Campo de Dalías in the south‐east of the Iberian Peninsula. In addition to this complexity one must consider the different levels with aquifer properties and their varying lithologies, which in some cases are in direct contact with the sea. Vertical sections based upon the various logs allow lateral correlation to be made between the anomalies detected, and provide information on the existence of both ascending and descending vertical flows, and the inflow of sea water into the system. Analysis of environmental isotopes (18O and D) indicate the areas of recharge with the greatest flow velocity. No seasonal variation in the isotopes was observed, which suggests that the residence time of the groundwater in the aquifer is several years. Radiocarbon dating gave estimates of generally long residence times, although in some sectors it is possible to detect the current recharge based on its tritium content, from rainwater infiltration or seawater intrusion. Copyright © 2002 John Wiley & Sons, Ltd.

Is the forward problem of ground water hydrology always well posed?

Complex aquifer systems are often modeled with quasi-three-dimensional models, which consider two-dimensional horizontal flow in the aquifers and one-dimensional vertical flow through aquitards. When the aquifer system consists of a phreatic aquifer and one or more semiconfined aquifers connected by aquitards, the discrete model consists of a nonlinear system of algebraic equations, because the transmissivity of the phreatic aquifer depends on the phreatic head. If the water extraction is very high, the phreatic aquifer can be depleted and the equations of the model must be modified accordingly. There are not simple and general criteria to state if the phreatic aquifer is depleted before solving the system of equations. Therefore, the iterative procedures (e.g., relaxation methods), used to find the solution to the forward problem, must handle these particular conditions and can suffer several problems of convergence. These problems can be caused by the choice of the initial head values or of the relaxation coefficient of the iterative algorithms; however, they can also be caused by the nonexistence or nonuniqueness of the solution to the system of nonlinear equations. The study of existence and uniqueness of the general problem is very difficult and, therefore, we consider a simplified problem, for which the discrete model can be handled analytically. The results of the numerical experiments show that the solution to the forward problem can be nonunique. Only for some cases it is possible to invoke physical arguments to eliminate tentative solutions.

Groundwater Modelling in Aquifers with highly Karstic and Heterogeneous Characteristics (KHC) in Palestine

Groundwater modelling is hindered by the lack of adequateinformation about the groundwater system and hence theneed for an interactive and efficient system for datapreparation and results analysis. Such a lack ofinformation usually necessitates the use of tediousiterative methodology within a sensitivity analysisscheme. The heterogeneous aquifer systems complicate theissue since more data is required to simulate the system.This study demonstrates the integrated approach to bridgethe gap between data handling and modelling. The karstcretaceous aquifer system (complex aquifer system) of theEastern Basin in the West Bank is used to illustrate thisapproach. The groundwater modelling approach integrates the outputsfrom different programs for data preparation andanalysis. These include (1) Groundwater Database (GWW)(2) Geographic Information System (GIS) (3) GroundwaterModelling System (GMS). In addition, the paper will summarize the data collectionefforts, problems faced and experience gained workingwith heterogeneous media. This involves linking theresults from various field investigations for groundwaterdevelopment programs in the West Bank.

Simulating groundwater flow and runoff for the Oro Moraine aquifer system. Part II. Automated calibration and mass balance calculations

A steady-state groundwater model of the Oro Moraine aquifer system in Central Ontario, Canada, is developed. The model is used to identify the role of baseflow in the water balance of the Minesing Swamp, a 70 km 2 wetland of international significance. Lithologic descriptions are used to develop a hydrostratigraphic conceptual model of the aquifer system. The numerical model uses long-term averages to represent temporal variations of the flow regime and includes a mechanism to redistribute recharge in response to near-surface geologic heterogeneity. The model is calibrated to water level and streamflow measurements through inverse modeling. Observed baseflow and runoff quantities validate the water mass balance of the numerical model and provide information on the fraction of the water surplus that contributes to groundwater flow. The inverse algorithm is used to compare alternative model zonation scenarios, illustrating the power of non-linear regression in calibrating complex aquifer systems. The adjoint method is used to identify sensitive recharge areas for groundwater discharge to the Minesing Swamp. Model results suggest that nearby urban development will have a significant impact on baseflow to the swamp. Although the direct baseflow contribution makes up only a small fraction of the total inflow to the swamp, it provides an important steady influx of water over relatively large portions of the wetland. Urban development will also impact baseflow to the headwaters of local streams. The model provides valuable insight into crucial characteristics of the aquifer system although definite conclusions regarding details of its water budget are difficult to draw given current data limitations. The model therefore also serves to guide future data collection and studies of sub-areas within the basin.

Nitrates as indicators of aquifer interconnection. Application to the Campo de Dalías (SE - Spain)

Relatively high concentrations of NO3 usually have their origin in processes of organic pollution and excessive use of inorganic fertilizers. In the case of agricultural areas, these activities may generate great quantities of nitrates. This fact has enabled us to use the nitrate ion to characterize an exploited aquifer unit of a very complex aquifer system, as is the case for the Campo de Dalias aquifer system (SE Spain). The shallow boreholes, which draw water from intensively cultivated superficial formations, yield waters with a high NO3 content. When the boreholes are deeper and penetrate low-permeability formations in the superficial layers, the waters contain little NO3; similar to what happens in areas of recharge where agricultural activities are absent. In addition, using longitudinal sections, it is possible to demonstrate the possible existence of connections between superficial and deep aquifers using NO3 as a tracer. Similarly one can locate those sectors responsible for contamination caused by the poorly lined boreholes themselves, when they perforate more than one aquifer in a multiple aquifer formation.

Direct-Formulation Finite Element (DFFE) Method for Groundwater Flow Modeling: Two-Dimensional Case

Real-world groundwater modeling deals with heterogeneous and anisotropic aquifer systems. Numerical models, particularly the finite difference and finite element methods, are extensively used for modeling such a complex aquifer system. The finite difference method is an age-old straightforward approach, whereas the finite element method is more idealistic, relatively new, and has emerged as a popular approach. The unique advantages with the finite element method are (i) an irregular-shaped domain can be discretized into elements with a matching boundary, (ii) a node can be connected with the neighboring nodes in any direction. Thus, the finite element analysis allows water/solute to flow more freely toward the surrounding nodes along nodal links. On the other hand, the mathematical formulation of the finite element technique follows a set of rules step by step. Conventionally, this idealistic approach uses shape functions and integration techniques to develop element matrices, which, in turn, are assembled to form the global matrix. This conventional global matrix was found to be inconsistent with the basic partial differential equation representing the mass balance in a nodal domain as a control volume. As a result, the matrix solution, particularly for nonlinear problems (e.g., vadose zone flow, density dependent flow, and so forth) becomes unstable and computationally burdensome. To overcome the limitations of the conventional finite element method for real-world groundwater modeling, a new approach, called the direct-formulation finite element (DFFE) method, has been developed. In this approach, a two-dimensional model domain is discretized into triangular elements. Element matrices are formed directly based on flow principles and material properties of elements without using shape functions and integration process. The DFFE method is robust. The global matrix is consistent, and the solution is stable and efficient. The results obtained from this approach were found in a good agreement with that obtained from analytical and other widely used models.

Hydrogeology of the Brunswick (Passaic) Formation and Implications for Ground Water Monitoring Practice

AbstractFractured shales of the Brunswick Formation provide a major aquifer in the most industrialized region of New Jersey. Numerous cases of ground water contamination have been documented in this formation. However, effectiveness of monitoring and remediation efforts is often hampered by the use of inappropriate concepts regarding ground water flow controls in this complex aquifer system. One such concept presumes that near‐vertical fractures parallel to the strike of beds provide principal passages for the flow and produce an anisotropic response to pumping stress. Field evidence presented in this paper confirms that the Brunswick Formation hosts a gently dipping, multiunit, leaky aquifer system that consists of thin water‐bearing units and thick intervening aquitards. The water‐bearing units are associated with major bedding partings and/or intensely fractured seams. Layered heterogeneity of such a dipping multiunit aquifer system produces an anisotropic flow pattern with preferential flow along the strike of beds. Within the weathered zone, the permeability of the water‐bearing units can be greatly reduced. The commonly used hydrogeologic model of the Brunswick as a one‐aquifer system, sometimes with vaguely defined “shallow” and “deep” zones, often leads to the development of inadvertent cross‐flows within monitoring wells. If undetected, cross‐flows may promote contaminant spread into deeper units and impair the quality of hydrogeologic data. Hydrogeologic characterization of the Brunswick shales at any given site should be aimed primarily at identification of the major water‐bearing and aquitard units. Recommended techniques for this characterization include fluid logging and other in‐well tests.

Simulation of regional subsurface flow by finite element models

The numerical models represent very useful tools for the simulation of regional flows and may provide several indications as to a rational management and allocation of the available water resources. The very complex aquifer systems underlying the Friuli-Venezia Giulia Region in northeastern Italy, has been analysed with the aid of two combined models based on the finite element method. The first model simulates the steady flow in the Upper Plain and relies on the Dupit-Forchheimer—Boussinesq approach. The second one simulates the multi-aquifer basin of the Lower Plain and is based on the integro-differential theory of flow. Both models have been run under a series of realistic assumptions properly combined with the limited available information. The results obtained for the dry regime are moderately satisfactory and allow for the first-hand appraisal of the quantity involved in the overall regional groundwater balance. They also point out the need for a substantial improvement in the quality and quantity of the regional subsurface data vis à vis reliable future predictions in a wider framework of practical interest.

Groundwater development, Kharga Oases, Western Desert of Egypt: A long-term environmental concern

The groundwater reserves in Kharga Oases have been studied for the long-term socioeconomic development in the area. The Nubian Sandstone, which consists of a thick sequence of coarse clastic sediments of sandstone, sandy clay interbedded with shale, and clay beds, forms a complex aquifer system. The Nubian Aquifer has been providing water to artesian wells and springs in the Kharga Oases for several thousand years.

Long-Term Effects of In-Situ Leach-Mining Restoration in Oakville Aquifer System near George, West Texas, with Implications for Shallow Waterflooding: ABSTRACT

The Miocene Oakville Formation is a major Gulf Coast freshwater aquifer and uranium host. The impact of long-term pumping during the restoration phase of leach mining depends on the efficiency of water-quality improvement methods, characteristics of the aquifer, and meteorological fluctuations affecting recharge. Newly acquired data from this industry have improved understanding of fluid migration in a fluvial depositional system. Development of the in-situ leach-mining industry has added vast amounts of subsurface hydrogeological data obtained from operation of an extensive network of wells. Both surface and subsurface data were combined in this investigation, which included analysis and interpretation of outcrop samples, uranium drill logs, cross sections loaned by companies, End_Page 1424------------------------------ pumping test data, water-well data furnished by the Texas Department of Water Resources, and geological and soils maps. This information was incorporated into the U.S. Geological Survey three-dimensional finite-difference computer model to predict ground-water behavior in a heterogeneous and anisotropic aquifer. Results indicate leakage through confining beds and communication across growth faults, suggesting that the Oakville is a complex aquifer system rather than a simple confined aquifer. Understanding the development of intricate flow paths and controlled movement of fluids through designed and controlled systems may improve methods of shallow waterflooding of petroleum reservoirs as well as management of water resources. End_of_Article - Last_Page 1425------------

The hydrogeological and geotechnical parameters as agents for gully-type erosion in the Rain-Forest Belt of Nigeria

The Agulu-Nanka gully complex is located in Anambra State, Nigeria. The gullies formed by erosion have damaged the environment extensively and driven people from homes and farm lands. The rate of growth of the gully system is estimated to be about 30 m per year. Earlier studies attributed the genesis and growth of the gullies to human activities and geomorphological processes. This study shows that the root causes of the gully genesis and growth strongly lie in the hydrogeological and geotechnical properties of a complex aquifer system. These properties are related to the high hydrostatic pressures in aquifers that reduce the effective stress of unconsolidated coarse sands, thereby leading to erosion. On the basis of the hydrogeological and geotechnical data available, it is suggested that a major dewatering scheme would check the growth of the gullies and also better supply water to the rural communities.

An efficient procedure in the digital simulation of aquifer systems

The simulation of complex aquifer systems by iterative solutions of the relevant equations involves the estimation and storage of several intermediate arrays of numbers. These occupy extensive memory and large storages. This has encouraged the authors to develop an optimization which is efficient in terms of memory required. The program code developed for the technique is tested using a strongly implicit procedure on a two-dimensional aquifer system. The results showed a saving of ∼ 98% in the core memory utilization.

Robert R. Bennett memorial to GIFT fund

The many personal friends, colleagues, and professional associates of the late Robert R. Bennett have joined in establishing a memorial in his honor. In recognition of his vigorous support of the American Geophysical Union, they have contributed in his memory to AGU's ‘Girding for Tomorrow’ program. His name will be inscribed on a list of honorees that will be displayed on a plaque in the AGU headquarters in Washington, D.C.Bennett, who received his M.S. in geology from the University of Nebraska in 1939, formerly directed groundwater research in the Water Resources Division of the U.S. Geological Survey. He was nationally and internationally recognized as an outstanding scientist in hydrogeology and groundwater hydrology. He was a pioneer authority in the development and application of analog‐ and digital‐computer simulations that aid in the analysis and prediction of the responses of highly complex aquifer systems to stresses imposed by man's development and utilization. He conducted basic research in petrophysics to define the fundamental principles governing permeability distribution and its directional characteristics and to elucidate the manner in which the permeability factor controls the movement of water in aquifer systems. He tested the applicability of the concepts he developed with prototype studies of the Ten‐sleep sandstone in the Big Horn Basin of Wyoming and of the Carrizo sandstone in the Coastal Plain of Texas.